Electronic and semiconductor components are used in ever-increasing numbers of consumer and commercial electronic products, communications products and data-exchange products. Examples of some of these consumer and commercial products are televisions, computers, cell phones, pagers, palm-type or handheld organizers, portable radios, car stereos, or remote controls. As the demand for these consumer and commercial electronics increases, there is also a demand for those same products to become smaller and more portable for the consumers and businesses.
As a result of the size decrease in these products, the components that comprise the products must also become smaller and/or thinner. Examples of some of those components that need to be reduced in size or scaled down are microelectronic chip interconnections, semiconductor chip components, resistors, capacitors, printed circuit or wiring boards, wiring, keyboards, touch pads, and chip packaging.
When electronic and semiconductor components are reduced in size or scaled down, killer defect sizes are significantly reduced per the required critical dimensions of the device. Thus, the defects that are present or could be present in the larger component should be identified and corrected, if possible, before the component is scaled down for the smaller electronic products.
In order to identify critical defects in electronic, semiconductor and communications components, the components, the materials used and the manufacturing processes for making those components should be broken down and analyzed. Electronic, semiconductor and communication/data-exchange components are composed, in some cases, of layers of materials, such as metals, metal alloys, ceramics, inorganic materials, polymers, or organometallic materials. The layers of materials are often thin (on the order of less than a few tens of angstroms in thickness). In order to improve on the quality of the layers of materials, the process of forming the layer—such as physical vapor deposition of a metal or other compound—should be evaluated and, if possible, modified and improved.
In order to improve the process of depositing a layer of material, the surface and/or material composition must be measured, quantified and defects or imperfections detected. In the case of the deposition of a layer or layers of material, its not only the actual layer or layers of material that should be monitored but also the material and surface of that material that is being used to produce the layer of material on a substrate or other surface that should be monitored. For example, when depositing a layer of metal onto a surface or substrate by sputtering a target comprising that metal, the target must be monitored for uneven wear, target deformation, target deflection and other related conditions. Uneven wear of a sputtering target is inevitable, a function of the magnet design and will reduce the lifetime of the target, and in some cases result in little or no deposition, of the metal on the surface of a substrate.
In conventional flat design sputtering targets (for example, targets used in the ALPS® sputtering chamber and/or the ENDURA® PVD system for 300 mm wafers, which are herein referred to generally as 300 mm ALPS or 300 mm ENDURA), there are three main types—each with advantages and disadvantages. For the first type, the target and backing plate are solder-bonded, with epoxy, indium and/or tin used for bonding. Soldering is a low cost, easy and low temperature operation, which preserves structure, but it has the disadvantage of a low bond strength for high chamber power. The second type has a diffusion bonded target/backing plate assembly where there is diffusion bonding along the entire target/backing plate interface (by hipping, forging, explosion bonding, etc). Diffusion bonding provides a strong bond, but the diffusion bonding process involves high temperature which destroys or significantly affects the ultrafine or submicron structure of the target, such as that obtained by ECAE. Also excessive warping, debonding or cracking is observed during the cooling phase of diffusion bonding in target and backing plate materials with incompatible CTEs (ceramic materials, chalcogenides, W to CuZn, thin blanks with high uniformity requirements such as Ni and Co). In the third type, a monolithic target is produced, which is relatively easy to manufacture, but requires strong, high purity material, that depends on the grain size, composition or both. Especially, in materials such as high purity aluminum and aluminum alloys, grain size needs to be less than 1 micron to provide enough strength for the use of a monolithic design. In that case grain refinement is obtained by severe plastic deformation using techniques such as Equal Channel Angular Extrusion (ECAE). Honeywell owned U.S. Pat. Nos. 5,590,389, 5,780,755, 6,723,187 or 6,908,517 describe the use of ECAE to produce sputtering targets with submicron or ultrafine grain sizes. For some extreme sputtering applications (high power, high water pressure), the monolithic target strength can be significantly tested, in particular in the flange area, which is the thinnest area.
Problems will occur when the sputtering target overheats because of the bombardment of the target with argon ions at a high power, which can often exceed a few to several tens of kilo-Watts. Such a high power can significantly affect the surface temperature of the PVD target without proper cooling and/or degrade the mechanical stability of the target if the cooling is inefficient. As mentioned, problems develop when using targets (especially aluminum and aluminum alloys) having very fine structures for high power sputtering applications. In monolithic designs, where a high strength submicron structure is needed, the submicron structure can lose some of its mechanical properties, because of the higher target temperatures leading to unacceptable warping. For diffusion or solder-bonded target designs, the higher temperatures/power creates excessive warping and potentially “debonding”, because of mismatch in the coefficient of thermal expansion between the target and backing plate material and degradation of mechanical properties of the backing plate materials. Diffusion and solder-bonding cannot provide targets with very fine grain sizes (less than 20 microns, for example, of a high purity aluminum PVD target), because heating treatments necessary to get a strong bond involve sufficiently high temperatures and cause the grain size to grow. There are four generally accepted factors that control the cooling of a sputtering target: a) thermal conductivity, b) cooling water flow rate, c) cooling surface area and d) the thickness of a target.
Cooling of the sputtering target can be improved by using a backing plate with a high thermal conductivity, increasing the cooling surface area, controlling the flow pattern of the coolant, improving coolant circulation with the rotating magnets and/or reducing the thickness of the target material. In the past, various attempts have been made to improve the cooling efficiency via various design modifications, but the most important “thickness factor” has not been considered for heat reduction. Therefore, in order to maximize the mechanical stability of sputtering targets while at the same time maximizing sputtering performance, researchers and technicians should review the cooling efficiency of the sputtering target.
Gardell et al. (U.S. Pat. No. 5,628,889) discloses a high-power capacity magnetron cathode with an independent cooling system for the magnet array support plate. In Gardell, a horizontal magnet array fluid control surface is physically attached to the magnet array support plate. The fluid control surface or device is not integrated into the materials of the support plate, the magnet array or the cathode materials. Therefore, there are more working parts, additional layers of complexity in the design and use of the magnetron cathode, and additional work for workers who handle repair and replacement of parts.
To this end, it would be desirable to develop and utilize a target assembly design that is: a) cost-efficient, b) easy to control, c) manufactured utilizing a method that provides good bond strength, such as a low temperature joining, coupling or bonding method, while the production of the target assembly d) does not degrade the microstructure of target and maintain the thermal/mechanical properties of target assembly.